Toroid core transformers, and methods of constructing transformers having toroid cores, have been known for many years. A toroid transformer is made by placing windings around a core having a toroid shape. Such windings require the conductor to be wound through the center "hole" of the toroid core. One typical arrangement is to have the primary wound on one-half the toroid (from 12:00 to 6:00 eg.) and the secondary (or other windings) wound on the remaining half.
Another typical arrangement has the primary, secondary, and etc. windings wound in layers (for example the primary winding may be a first layer and a secondary winding may be a second layer, or vice versa). Thicknesses of insulation are provided between windings to provide a dielectric between the various windings. The insulation is often layers of film which are wound through the center "hole" of the toroid core. Alternative winding constructions may include coaxial or bifilar conductors.
One advantage of toroid construction, relative to other physical constructions, is a reduction of material volumes needed for the core for a given electrical capacity. This reduces the weight and cost of the transformer. However, the equipment required to wind long conductor lengths on a toroid core is costly and complex. Additionally, the winding of the conductor and insulating films through the center hole of the toroidal core is labor intensive, thus increasing the cost of making the winding.
One type of toroidal transformer winding is called progressive winding. A progressive winding is one in which the coil is wound such that portions of a total winding are wound in a number of pie-shaped segments around the toroid. Each pie-shaped segment is comprised of an odd number of layers, and the even numbered layers are pitched in a direction opposite the direction of the pitch of the odd numbered layers. After the desired odd number of layers have been completed, the subsequent pie shaped segments of the toroid are wound, again by layers. This is repeated until the winding is complete. Progressive winding reduces the maximum turn to turn voltage gradient or stress on the conductor insulation.
While progressive winding reduces voltage stress, it results in problems when wound according to the prior art. Specifically, when the second layer of a particular segment is being wound, the end turns of the second layer tend to force the end turns of the first layer outward. This results in the windings having undesirable spacing and difficulty placing the maximum desired number of turns on a toroid for a given size toroid.
The inability to precisely place windings (particularly the end turns) or stack layers results in the disadvantage that the density of the windings, or the number of turns per square inch of coil cross section, is less than the maximum possible. If the turns aren't placed as densely as possible, then additional layers must be provided to accommodate the desired number of turns, and the initial hole in the center of the toroid core must have a greater diameter. This necessarily results in a greater length of the core magnetic path and a greater core volume and weight. The increase core volume and weight results in increased material costs. Also, the equipment to wind the toroid core must be able to pass through the "hole" of the toroid. Thus, it is helpful to have the turns placed as densely as possible to keep the center "hole" large enough for the winding equipment to pass therethrough.
There are numerous insulation configurations and winding techniques for toroid transformers in the prior art. Known insulation configurations include the use of molded jackets, molded insulation parts having features that place individual conductors in specific locations, and flexible film insulating the core. Two known winding techniques include programming winding equipment to locate conductors on molded insulation and flexible film insulation separating multi-coil windings by thicknesses of the film insulation.
However, each of these prior art techniques and/or apparatuses do not provide a way to specifically anchor or hold in place the pie-shaped segments of progressive windings. The lack of anchoring these progressive winding section results in the spreading of the section, particular when winding multiple layers in the section.
Accordingly, it is desirable to have a transformer and a method of winding a transformer that provides for progressive winding without spreading of the lower layers of windage. Such a method and apparatus should be relatively simple and low cost, with a reduced labor content. It is also desirable to provide a transformer and a method of winding a transformer that provides a greater density of windings per square inch of core cross section than the prior art methods. Such a method should also provide a toroidal transformer that has a relatively small center hole in the toroid and a shorter main length of the core magnetic path than prior art methods.
Electrical clearance and electrical creepage are two potential problems associated with transformers. Electrical clearance relates to the physical distance (through air) between windings. Insufficient electrical clearance, for a given voltage difference between windings, may result in electrical arcing between the windings. Electrical creepage refers to an electric "arc" that travels across surfaces between two windings. Industry standards exist for electrical clearance and creepage that require specified physical distances between windings for various voltage differences.
Accordingly, it is desirable to have a transformer, and method of making a transformer, that eliminates or reduces the use of film insulation between windings. Also, sufficient air clearance between windings should be provided. Preferably creepage distances across surfaces will be sufficient